The syntax is quite complex for the two relative clauses in this verse. Since 1852 the LDS text has interpreted Lamanites as a possessive form (by the addition of the apostrophe in the 1852 edition), while the earlier text and the current RLDS text have the basic noun Lamanites. Neither reading works fully.
One problem is the noun flight. The possessive usage Lamanites’ implies that the Lamanites too were fleeing, which is not the case. Elsewhere in the text, the noun flight always refers to the act of fleeing (including the first use of flight in this verse: “we did again take to flight”). But if we interpret the second and third occurrences of flight in Mormon 5:7 as deriving from the verb fly rather than flee, then we could interpret flight in Mormon 5:7 as meaning ‘swift movement in general’ (see definition 2 in the Oxford English Dictionary under the noun flight derived from the verb fly). Under this interpretation, the ellipted noun after the possessive Lamanites’ would take the more general meaning of ‘speed’ rather than ‘fleeing’.
The problem with the basic noun Lamanites is that the actual meaning seems to be that those that escaped were “swifter than the Lamanites”; that is, the use of flight seems unnecessary. In fact, the original subject-verb agreement for this passage provides some support for this interpretation:
If we substitute who for whose flight, we get the perfectly sensible “and they who were swifter than the Lamanites did escape”; in other words, the plural were in the relative clause agrees with the earlier they, not flight. (The critical text, as expected, will restore the original they and were as well as maintain, of course, the original noun phrase whose flight.)
Similarly, the last occurrence of flight (“whose flight did not exceed the Lamanites”) defi- nitely seems to need some qualification in order to state that the speed of the Nephites’ flight did not exceed the speed of the Lamanites. The verb exceed usually deals with such situations by using that of after exceed:
If we apply this interpretation, but without the that of, to Mormon 5:7, we end up once more with a reference to “the flight of the Lamanites”, which is a problem since, as already noted, flight otherwise refers only to ‘fleeing’ in the Book of Mormon text.
Another question is whether the Book of Mormon text has isolated possessive forms of nouns (that is, without the following modified noun). The answer is, not very often:
We note that one of these examples directly quotes the Bible, and the expression “I am the Lord’s” is also biblical (see Isaiah 44:5). So there is only one example (Mosiah 13:5) that could be said to represent the actual Book of Mormon language style. (As explained under Mosiah 13:5, the corresponding passage in Exodus 34 refers to Moses’s face shining; it does not refer to his whole body shining. The possessive form Moses’ is undoubtedly correct in Mosiah 13:5.)
When we turn to cases of the possessive pronoun without a following noun, we find 19 instances in the text (of which eight are related to quotations from the King James Bible). And there is one case after the subordinate conjunction than:
So we have evidence of the isolated possessive after than —in addition to the possible possessive reading here in Mormon 5:7 of “swifter than the Lamanites’ ”.
Alison Coutts (personal communication) suggests another possibility for ellipsis here in Mormon 5:7, namely, the noun pursuit, as if the text read as follows:
Under this analysis, the possessive Lamanites’ would be correct. One problem with this interpretation, however, is that there is no other instance in the text where ellipsis involves the antonym for a preceding word. If the possessive form Lamanites’ is correct, then the more reasonable ellipsis should be something like a more general meaning for the noun flight (as discussed above). Ultimately, the question comes down to whether flight can mean ‘speed’ in Mormon 5:7. My own inclination is to reject such an interpretation since flight never has this general meaning elsewhere in the text. This means, then, that the possessive interpretation Lamanites’ should also be rejected.
Summary: Restore the original basic noun form Lamanites both times in Mormon 5:7 since the text is not referring to “the flight” of the Lamanites; it seems doubtful that the ellipted word flight can here be assigned the general meaning ‘speed’ since that meaning appears nowhere else in the Book of Mormon.